1. Field of the Invention
The present invention generally relates to a coil spring assembly of an elastic connecting mechanism. More specifically, the present invention relates to a coil spring assembly for a lock-up damper of a torque converter.
2. Background Information
Torque converters usually include a fluid coupling mechanism for transmitting torque between the crankshaft of an engine and the input shaft of an automatic transmission. In recent years, to improve fuel efficiency, some torque converters have included a lock-up device that, upon reaching predetermined operating conditions, lock-up the torque converters so that power from the crankshaft of an engine is directly transmitted to the automatic transmission, bypassing the fluid coupling device. Upon engagement, lock-up devices often cause a shudder, or vibration. Further, while engaged, the lock-up device is subject to vibrations caused by sudden acceleration, or deceleration, or other vibration including circumstances associated with internal combustion engines. Consequently, torsional vibration dampening apparatus' are typically employed in lock-up mechanisms to dampen vibration.
A torque converter has three types of runners (impeller, turbine, stator) located inside for transmitting the torque by means of an internal hydraulic oil or fluid. The impeller is fixedly coupled to the front cover that receives the input torque from the power input shaft. The hydraulic chamber formed by the impeller shell and the front cover is filled with hydraulic oil. The turbine is disposed opposite the front cover in the hydraulic chamber. When the impeller rotates together with a front cover, the hydraulic fluid flows from the impeller to the turbine, resulting in a rotation of the turbine. As a result, a torque from the turbine is transmitted from the turbine to the main drive shaft of the transmission.
The lock-up clutch or lock-up damper has a clutch function to connect or disconnect the front cover, and a dampening function to absorb and attenuate torsional vibration included within torque. When the lock-up clutch is connected, torque is transmitted to the turbine mechanically, not via the hydraulic fluid. The lock-up clutch is disposed in the space between the front cover and the turbine. As mentioned above, the lock-up clutch is a mechanism to directly transmit the torque between the crankshaft of the engine and the drive shaft of the transmission by mechanically coupling the front cover and the turbine together.
The lock-up clutch primarily includes a piston and an elastic coupling mechanism (dampening mechanism) to connect the piston to the drive members on the power output side of the turbine. The piston is a disk-shaped member, which is axially movable within the torque converter. The piston is disposed in the space between the front cover and the turbine to divide the space into a first hydraulic chamber on the front cover side and a second hydraulic chamber on the turbine side. As a result, the piston can move close to and away from the front cover in response to the pressure difference between the first hydraulic chamber and the second hydraulic chamber. A friction joining member covered with a friction facing is formed on the axial surface of the front cover which faces the piston. Preferably, the friction facing is located at the outer periphery of the axial surface of the cover. When the lock-up clutch is engaged, the hydraulic oil in the first hydraulic chamber is drained from its inner circumferential side of the torque converter and the hydraulic oil is supplied to the second hydraulic chamber. As a result, the hydraulic pressure in the second hydraulic chamber becomes greater than the hydraulic pressure in the first hydraulic chamber. This pressure differential between the first and second hydraulic chambers causes the piston to move toward the front cover of the torque converter such that the piston engages the cover. This movement of the piston causes the friction facing of the piston to strongly press against the friction surface or facing of the front cover.
The elastic coupling mechanism of the lock-up clutch functions as a torsional vibration dampening mechanism to dampen vibrations in the lock-up clutch. The elastic coupling mechanism includes, for example, a drive member or retaining plate fixedly coupled to the piston, a driven member fixedly coupled to the turbine, and an elastic member, such as one or more coil springs, disposed in between the drive member and the driven member to enable torque transmission therebetween.
A spring seat is disposed at each end of the coil springs in the circular direction. The spring seat typically includes a seat part and a protrusion. The seat part includes a first face with which the end of the coil spring is in contact, and a second face, which is in contact with the connecting parts of the retaining plate and the driven plate. The protrusion extends from the seat part of the spring into the inside of the coil spring.
In the elastically coupling mechanism of the above mentioned conventional lock-up device, a gap is formed between the protrusion of the spring seat and the inner diameter of the coil spring. Thus, the spring seat can move freely against the coil spring owing to the gap.
Therefore, the following problems often occur in the above mentioned conventional lock-up device. When torsional vibration is inputted in the lock-up device, the coil spring repeats a motion of compression and recovery in a circular direction. Since the spring seats can move freely against the coil spring, the motions of the spring seats and the coil spring tend to be unstable when torsional vibration is transmitted during an ultra high speed or an ultra high load. As the result, the performance of the coil spring to absorb a vibration is reduced.
In view of the above, there exists a need for coil spring assembly which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.